Vulnerability CVE-2026-39858: Information
Description
Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, there is a high severity authentication bypass vulnerability in Traefik's ForwardAuth and snippet-based authentication middleware. Traefik's forwarded-header sanitization logic targets only canonical header names (e.g., X-Forwarded-Proto) and does not strip or normalize alias variants that use underscores instead of dashes (e.g., X_Forwarded_Proto). These unsanitized alias headers are forwarded intact to the authentication backend. When the backend normalizes underscore and dash header forms equivalently, an attacker can inject spoofed trust context — such as a trusted scheme or host — through the alias headers and bypass authentication on protected routes without valid credentials. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.
Fixed packages
Package name | Branch | Fixed in version | Version from repository | Errata ID | Task # | State |
|---|---|---|---|---|---|---|
| traefik | sisyphus | 3.6.15-alt1 | 3.6.15-alt1 | ALT-PU-2026-7142-5 | 417190 | Fixed |
| traefik | sisyphus_riscv64 | 3.6.15-alt1 | 3.6.15-alt1 | ALT-PU-2026-7534-1 | - | Fixed |
| traefik | sisyphus_loongarch64 | 3.6.15-alt1 | 3.6.15-alt1 | ALT-PU-2026-7499-1 | - | Fixed |
| traefik | p11 | 3.6.15-alt1 | 3.6.15-alt1 | ALT-PU-2026-7164-5 | 417230 | Fixed |
| traefik | c10f2 | 3.6.15-alt1 | 3.6.15-alt1 | ALT-PU-2026-7154-5 | 417229 | Fixed |
References to Advisories, Solutions, and Tools
Hyperlink | Resource |
|---|---|
| https://github.com/traefik/traefik/releases/tag/v2.11.43 |
|
| https://github.com/traefik/traefik/releases/tag/v3.6.14 |
|
| https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2 |
|
| https://github.com/traefik/traefik/security/advisories/GHSA-5m6w-wvh7-57vm |
|
| BDU:2026-06478 | |
| GHSA-5m6w-wvh7-57vm |